The present invention relates to a resin composition having an excellent vibration-damping property and, more particularly, to a vibration-damping resin composition suitably adapted as a vibration-damping layer in a vibration-damping composite metal plate.
With recent developments in transportation systems and coexistence of factories and offices with living areas, the problems of noise and vibration generated by various vehicles, machines or apparatuses have become acute from the viewpoints of hygiene and environment. Demand for solution of these problems has become strong. In particular, there is a strong demand for parts such as an oil pan or an engine cover for shielding engine noise from vehicles, and parts for shielding noise from home electrical equipment and metal processing machinery.
As one measure against noise, the user of a vibration-damping composite metal plate such as a vibration-damping composite steel plate has been proposed. The composite metal plate damps vibration by internal friction due to shear deformation of a viscoelastic material of an interlayer of the plate. The composite metal plate is used to surround a noise source. For this reason, the composite metal plate is used in a plate form, and is also formed into a desired shape by, e.g., bending or drawing.
The material of the interlayer of the vibration-damping composite metal plate is conventionally selected from thermoplastic or thermosetting resins. Examples of thermoplastic resins include polymers such as a vinyl acetate resin or a vinyl chloride resin; copolymers such as a vinyl acetate-ethylene copolymer or an acrylonitrile-styrene copolymer; or compositions thereof with a plasticizer. Examples of thermosetting resins include an urethane resin or an epoxy resin.
A resin composition comprising a blend of two or more resin has also been proposed as the material of the interlayer. For example, Japanese Patent Publication No. 79-1354 discloses a composition obtained by adding a viscoelastic polymer such as polyurethane to an acidic copolymer such as an ethylene-acrylic acid copolymer or an ionomer thereof. Japanese Patent Laid-open No. 59-80454 discloses a composition obtained by adding an amorphous polymer to a crystalline polyolefin modified by an unsaturated carboxylic acid or an anhydride thereof.
Japanese Patent Laid-open No. 57-167360 discloses the water dispersion of a composition comprising a styrene-acrylic ester copolymer and a scaly inorganic powder.
A viscoelastic material conventionally used for an interlayer of a vibration-damping composite metal plate has a mechanical loss tangent tan .delta. which becomes maximum at a temperature higher than its glass transition temperature. At this specific temperature, the rigidity of the viscoelastic material used is abruptly decreased, and the loss factor .eta. of the metal plate is not always good. The good vibration-damping property of a laminated structure such as a vibration-damping composite metal plate is closely associated with the good vibration-dampring property of the viscoelastic material used for the interlayer and the relatively high rigidity thereof. At the region of the low regidity of the viscoelastic material, its vibration-damping property can not be fully exhibited. When this specific temperature is high, the vibration-damping property is abruptly decreased. When two or more resins are blended, since the resins have compatibility, the glass transition temperature of the composition is decreased, and satisfactory vibration-damping property cannot be obtained at high temperatures.
No vibration-damping composite metal plates using a vibration-damping resin composition has satisfied both the requirements of good vibration-damping property and processability such as bending or deep drawing property. For this reason, a vibration-damping resin composition for a vibration-damping layer of a vibration-damping composite metal plate and having excellent vibration-damping property, processability and mechanical strength has been desired.